$\"\"$

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The trigonometric equation $\"\"$ and the interval is $\"\"$ .

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Apply formula: $\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ and $\"\"$

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$\"\"$ and $\"\"$

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$\"\"$ and $\"\"$ .

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$\"\"$

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Case 1:

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Solve the equation $\"\"$ .

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$\"\"$

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General solution of $\"\"$ is $\"\"$ .

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$\"\"$

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$\"\"$ .

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For $\"\"$ , $\"\"$

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For $\"\"$ , $\"\"$

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For $\"\"$ , $\"\"$ .

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$\"\"$

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Case 2:

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Solve the equation $\"\"$ .

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Sine is negative in third and fourth quadrants.

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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The solutions are $\"\"$ .

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The solution of the equation is $\"\"$ in the interval $\"\"$ .

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$\"\"$

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Graph of $\"\"$ is:

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$\"\"$

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Observe the graph of the function, the graph touches the $\"\"$ -axis at $\"\"$ .

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So, the solution is $\"\"$ in the interval $\"\"$ . $\"\"$

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The solution of the equation is $\"\"$ in the interval $\"\"$ .